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类型 基础研究 预答辩日期 2018-03-24
开始(开题)日期 2016-01-22 论文结束日期 2017-12-13
地点 动力楼422教室 论文选题来源 国家自然科学基金项目     论文字数 9.1 (万字)
题目 双氧水/铁基材料异相芬顿反应耦合氨基溶液同时脱硫脱硝机理研究
主题词 氨基溶液,H2O2,铁基材料,脱硫脱硝,反应机理
摘要 煤炭是我国最重要一次能源,燃煤发电在工业生产和生活用电中占有主要的地位。煤炭燃烧的过程中会释放多种污染物。典型的燃煤烟气污染物,如SO2、NO和NO2,在大气环境中会发生一系列化学反应,造成酸雨、光化学烟雾和臭氧层破坏等环境问题,对人类的生命健康产生严重的危害。目前,电厂燃煤锅炉通常采用选择性催化还原技术和石灰石石膏法湿法脱硫技术,分别脱除锅炉尾气中的氮氧化物和硫氧化物。由于上述单独脱除技术存在占地面积大,投资和运行成本高,失活催化剂作为固体废弃物难以处理等严重缺陷。因此,开发和研究多种污染物一体化协同脱除技术具有十分重要的理论意义和工程应用价值。本课题组提出了一种针对燃煤烟气中硫氧化物和氮氧化物的协同“分级吸收”工艺,即基于H2O2/铁基材料异相芬顿反应耦合氨基吸收溶液同时脱硫脱硝工艺。其过程可描述为,燃煤烟气中SO2在一级吸收塔中被氨基溶液吸收脱除,脱硫后的烟气与雾化的H2O2混合并通过催化反应器,实现对NO的高效氧化,氧化后的氮氧化物在二级吸收塔中被来自一级脱硫塔的氨基吸收溶液吸收脱除。基于该新工艺,本课题对液相吸收和气相氧化两个部分开展了实验和机理研究。 (1)该新工艺中两级吸收塔内的氨基溶液可以高效脱除烟气中SO2和NO2,但难以脱除NO。在自行搭建的鼓泡床内,探究了操作参数对氨基溶液脱除烟气中SO2和NO2的影响,并结合热力学计算数据和气液传质-反应动力学模型,揭示了氨基溶液脱除SO2和NO2的反应机理。一级吸收塔内的氨基溶液脱硫实验结果表明,在所有实验工况下,10wt.%的尿素溶液和5wt.%尿素/5wt.%亚硫酸铵溶液均能高效吸收烟气中的SO2,但对于NO的脱除效率较低。二级吸收塔内的氨基溶液脱除NO2实验结果表明,含有亚硫酸铵的氨基溶液可以高效脱除烟气中的NO2。产物的表征结果显示亚硫酸铵还原NO2是氨基溶液脱除NO2的主要反应。在NO2脱除试验的基础上,从热力学和动力学层面分别深入探讨了NO2脱除过程。在热力学层面,不同反应温度下的热力学数据显示,在20℃到90℃范围内,只有NO和NO2能在气相中能稳定存在,液相中亚硫酸铵直接还原HNO2和NO2生成N2是二级吸收塔中的主要脱硝反应。50℃溶液的NO2-H2SO3-NH3-H2O反应系统电位-pH图表明,在pH从-7到14的范围内,气相的NO2和液相的〖"NO" 〗_"2" ^"-" 均可被〖"SO" 〗_"3" ^"2-" 还原成N2。在动力学层面,采用经典的化学法和Danckwerts标绘测定了反应器的气液传质参数,基于双膜理论建立气液吸收动力学模型,计算了NO2的吸收速率和反应速率常数,结合八田数(Ha数)对NO2脱除过程进行了分析。动力学结果表明:5wt.%尿素/5wt.%亚硫酸铵溶液吸收NO2的反应为快速拟一级反应。通过拟合实验数据获得了NO2脱除反应的拟一级反应速率常数经验表达式及NO2吸收速率方程,NO2吸收速率方程可以较好地模拟NO2在氨基溶液中的脱除过程。 (2)该新工艺中将气相H2O2/Fe2O3异相芬顿反应预氧化系统和氨基溶液吸收系统耦合可以高效氧化并脱除烟气中NO,并深入探究了其中的催化机理。探究气相H2O2/Fe2O3异相芬顿反应耦合氨基溶液脱硝系统内关键操作参数对NO脱除效率的影响。在烟气流量为1.5L/min,NO浓度为530ppm,O2浓度为7%,催化剂用量为2g,H2O2溶液浓度为2mol/L,H2O2溶液进液速率为5mL/h,烟气预热温度为140℃,雾化温度为140℃,催化温度为140℃的实验条件下,2小时内基本保持78%的脱硝效率。在操作参数实验的基础上,根据液相产物分析和物质平衡计算推理了主要的脱硝反应路径。通过考察了Fe2O3/典型载体(Al2O3和SiO2)、典型含铁尖晶石(ZnFe2O4、NiFe2O4和CuFe2O4)以及典型含铁钙钛矿(LaFeO3和La0.85FeO3)的脱硝能力,对催化剂做了初步的探究和筛选。实验结果表明:钙钛矿类催化剂的脱硝性能较好。分别从自由基检测、热力学计算、产物采样分析、催化剂理化特性离线分析和机理反应动力学的角度,深入探讨了Fe2O3催化H2O2分解氧化NO的反应机理。自由基检测实验和自由基牺牲实验显示,催化剂表面生成的?OH是氧化脱除NO的关键。热力学计算和氧化实验结果表明,NO2和HNO3为主要氧化产物。基于现代表征手段(XRD、FTIR、SEM-EDX和XPS)分析了反应前后Fe2O3催化剂表面理化特性变化。XRD表征分析明确了催化剂的晶体结构在2小时反应期间保持稳定;XPS表征结果显示H2O2在Fe2O3上的分解遵循基于Fe的Haber-Weiss反应机理。“吸附-反应-脱附”的催化机理动力学研究表明NO氧化过程遵循H2O2吸附的Eley-Rideal催化反应模型,即NO的氧化反应是H2O2首先在催化剂表面吸附活化形成活性中间体,然后NO与活性中间体作用形成最终产物的过程。 (3)针对催化剂筛选实验中脱硝能力较好的含铁钙钛矿催化剂,制备并考察了钙掺杂镧铁钙钛矿La1-xCaxFeO3(x=0,0.1,0.3和0.5)的脱硝能力,建立了相应的构效关系,阐明了可能存在的两种表面催化机理。脱硝试验和氧化烟气中氮氧化物成分分析表明:随着催化剂中Ca掺杂量的增加,NO脱除效率降低,氧化烟气中的NO浓度增加,而NO2浓度和HNO3浓度降低。研究结果表明,Ca掺杂量的增加会降低镧铁钙钛矿的脱硝能力。通过KMnO4滴定和ESR光谱实验,考察了催化剂对H2O2分解速率和?OH浓度的影响,结果明确了随着Ca掺杂含量的增加促进了H2O2的分解,但却抑制了?OH的生成。基于多种现代表征手段,深入探究了Ca的掺杂后催化剂表面理化特性的变化,结果显示Ca掺杂量的增加导致镧铁钙钛矿表面氧空位浓度升高。基于对催化剂理化特性、?OH生成浓度、H2O2分解规律和脱硝效率的深入分析及关联,Ca掺杂对脱硝效率的抑制机理可阐述如下:在钙掺杂的镧铁钙钛矿上,H2O2通过基于氧空位的表面反应机理分解产生O2和H2O,该过程抑制了H2O2分解产生?OH的反应,造成NO脱除效率的降低。 (4)针对高硫烟气,考察了H2O2/Fe2(SO4)3异相芬顿反应耦合氨基溶液的脱硫脱硝能力,探究了高浓度SO2对于NO脱除的促进机理。操作参数优化实验显示:在SO2浓度为2000ppm,NO浓度为500ppm,O2浓度为7%,催化剂温度为140℃,H2O2浓度为1mol/L,H2O2流量为5mL/h,催化剂用量为2g的实验条件下,脱硫和脱硝效率分别为99.8%和92.5%。对比单独脱硝和同时脱硫脱硝实验显示,SO2的加入有利于NO的脱除。结合XPS表征分析对于其中的机理阐述如下:SO2促进了Fe2(SO4)3催化剂表面氧空位的形成,导致Fe(III)转化为Fe(II)。相比基于Haber-Weiss反应机理产生?OH的方式,"≡Fe" ("II" )"-OH" 催化分解H2O2产生?OH的速率更快,同时也消耗更少的H2O2,这说明在该反应体系中,SO2对于NO的协同脱除作用。针对连续12小时实验中脱硝效率下降的问题,SEM-EDX表征结果显示:Fe2(SO4)3催化剂在反应过程中严重的颗粒团聚可能是造成脱硝效率降低的主要原因。
英文题目 MECHANISM STUDY ON SIMULTANEOUS REMOVAL OF SO2 AND NO BY COMBINATION OF H2O2/IRON-BASED MATERIALS AND AMMONIUM-BASED SOLUTION
英文主题词 Ammonium-based solution, H2O2, Fe-based materials, SO2 and NO removal, Reaction mechanism
英文摘要 As the most important primary energy source in our country, coal-fired power generation plays a critical role in industrial production and household consumption. Multiple pollutants are released in the coal-fired process. Typical pollutants, such as SO2, NO and NO2, lead to serious environmental problems such as acid rain, photochemical smog and ozone layer destruction via a series of chemical reactions in the atmosphere. These serious environmental problems are harmful for human health. At present, the conventional selective catalytic reduction technology and wet flue gas desulfurization technology is commonly used to remove nitrogen oxides and sulfur oxides in coal-fired flue gas of power plant, respectively. There are still some serious disadvantages in these technologies such as large occupation, high investment and operating costs, difficulties in handling spent catalyst as solid waste. Consequently, it is of great importance to further develop simultaneous removal technology in one reactor or one set of reactors. Our group proposed a novel process for SO2 and NO removal in one set of reactors, that is "simultaneous removal of SO2 and NO with H2O2/Fe-based material coupled with ammonium-based absorbent". The whole process is described as follows. At first, SO2 is removed with ammonium-based absorbent in the first absorption tower. The flue gas after desulfurization is blended with the vaporized H2O2 and pass through a catalytic reactor. The NO in flue gas is oxidized into the high-valent nitrogen oxides. In the secondary absorption tower, the high-valent nitrogen oxides are removed with ammonium-based absorbent from the first absorption tower. In the aspects of liquid absorption and gas phase oxidation, the theoretical and experimental researches on the novel technique are carried out in this paper, respectively. (1) In this novel process, the SO2 and NO2 in the flue gas are easily removed by ammonium-based solution rather in scrubber but NO is rarely removed. In the self-designed bubbling scrubber, the effect of operation parameters on the SO2 and NO2 removal with ammonium-based solution is investigated and the mechanism is revealed with the thermodynamic calculation and kinetic model. For the desulfurization experiments in the first tower, experimental results indicate that both 10 wt.% urea solutions and 5 wt.% urea / 5 wt.% ammonium sulfite solutions have a good performance on SO2 removal rather than NO removal. For the NO2 removal experiments in the second tower, the content of ammonium sulfite in ammonium-based solution is the crucial factor in NO2 absorption. The characterization of product indicates that the reduction reaction between NO2 and ammonium sulfite is the main approach for NO2 absorption. On the basis of NO2 removal experiments, the mechanism is intensively discussed in aspects of thermodynamics and kinetics. In the aspect of thermodynamic study, the results of thermodynamic calculations in different temperature indicate that only NO and NO2 are stable in the range of 20℃ ~ 90℃ and the direct reduction of NO2 or HNO2 with ammonium sulfite is the main NO2 removal reaction. The NO2-H2SO3-NH3-H2O reaction system potential-pH plot (at 50℃) showed that, in the pH range from -7 to 14, both NO2 in gas phase and 〖"NO" 〗_"2" ^"-" in liquid phase can be removed by SO2, producing 〖"SO" 〗_"4" ^"2-" and N2. In the aspect of kinetic study, the gas-liquid mass transfer parameters of reactor are determined by the chemical method and Danckwerts plotting. On the basis of the two-film theory, the NO2 absorption rate equation is established. The NO2 absorption rate and reaction rate is calculated. The NO2 removal process is analyzed with Hatta number. According to the experimental results, the NO2 absorption with 5wt.% urea / 5wt.% ammonium sulfite is verified as a fast pseudo-first-order reaction. An empirical expression for the pseudo-first-order reaction rate constant for NO2 removal is established. The empirical expression for the first order reaction rate constant and NO2 absorption rate are obtained by fitting experimental data. The NO2 absorption rate equation can be used to simulate the NO2 absorption rate in 5wt.% urea / 5wt.% ammonium sulfite in bubbling bed. (2) In this novel process, NO can be efficiently oxidized and removed in H2O2/Fe2O3 heterogeneous Fenton reaction coupled with ammonium-based solution and the catalytic mechanism is intensively discussed. The effects of operation parameters on NO removal are intensively studied in a self-designed bench-scale device. The denitrification efficiency keeps 78% in 2 hours, under the operation conditions where the flue gas flow rate is 1.5 L/min, NO concentration is 530 ppm, O2 concentration is 7%, catalyst dosage is 2 g, H2O2 concentration is 2 mol/L, H2O2 feeding rate is 5mL/h, flue gas preheating temperature is 140℃, vaporization temperature is 140℃, catalytic temperature is 140℃. On the basis of material balance calculation, the possible denitrification process is speculated. The NO removal experiments with Fe2O3 / typical supports (Al2O3 and SiO2), typical Fe-based spinel (ZnFe2O4, NiFe2O4 and CuFe2O4) and typical Fe-based perovskite (LaFeO3 and La0.85FeO3) is premiere presented. It is indicated that the Fe-based perovskite has a better performance on NO removal than other catalysts. The NO oxidation with H2O2 / Fe2O3 is studied in aspects of free radical capture, thermodynamic calculation, analysis of gas-liquid two-phase products, the physicochemical property of catalyst and kinetics study. On the basis of experimental results, the catalyst mechanism on H2O2 / Fe2O3 system is studied and investigated in depth. The free radical capture and scavenger experiments indicate that the ?OH plays a critical role in NO removal. The thermodynamic calculation and the analysis of product show that the main oxidation products are HNO3 and NO2. The characterization (XRD, FTIR, SEM-EDX and XPS) of fresh and spent catalyst indicates the changes of physicochemical property. The XRD characterization indicates that the crystal structure of catalyst is robust in 2 hours’ reaction. The XPS spectra of catalysts show that the catalytic decomposition of H2O2 over Fe2O3 follows the Haber-Weiss mechanism. According to 4 kinds of catalytic kinetic model (adsorption - reaction - desorption) and the fitting of experimental data, it is proved that the NO oxidation follows the Eley-Rideal catalytic reaction model, that is, the H2O2 adsorbed on the catalyst surface and subsequently, NO is oxidized by active product. (3) Due to the good performance of typical Fe-based perovskite in NO removal, La1-xCaxFeO3 (x=0, 0.1, 0.3 and 0.5) is prepared and studied in NO removal experiments. The structure-activity relationship is established and the two kinds of surface catalytic mechanism is elucidated. The NO removal experiments and oxidaiotn product analysis show that, with the Ca doping amount increased, NO concentration in the oxidized flue gas increases while the NO2 and HNO3 concentrations decrease, leading to the decreased NO removal efficiency. It is clear that the doped Ca can weaken the NO removal ability of La1-xCaxFeO3 (x=0, 0.1, 0.3 and 0.5). According to the ESR spectra and the KMnO4 titration test, the doped Ca accelerates H2O2 decomposition without produce ?OH. According to the characterization of catalyst surface physicochemical property, the surface oxygen vacancy of La1-xCaxFeO3 (x = 0.1, 0.3, and 0.5) increased a lot with the Ca doping amount increased. According to the intensive discussion and correlation of catalyst physicochemical property, ?OH generation concentration, H2O2 decomposition rate and NO removal efficiency, the inhibition mechanism of doped Ca on NO removal can be elucidated as follows. On the La1-xCaxFeO3 (x=0, 0.1, 0.3 and 0.5), the decomposition of H2O2 over surface oxygen vacancies via superficial mechanism produces O2 and H2O instead of ?OH production via Habber-Weiss mechanism, which is the main factor for the declined NO removal efficiency. (4) For the high-sulfur flue gas, the desulfurization and denitrification from the with H2O2 / Fe2(SO4)3 coupled with ammonium-based solution is carried out and the improvement mechanism of high SO2 concentration on NO removal is studied. Under the conditions of 2000 ppm SO2, 500 ppm NO, 7% O2, catalyst temperature of 140℃, H2O2 concentration of 1 mol/L, H2O2 feed rate of 5 mL/h and 2 g catalyst, the SO2 and NO efficiency is 99.8% and 92.5%, respectively. The comparison between separate NO removal and simultaneous SO2 and NO removal indicates that the additive SO2 is benefit for the NO removal. The XPS spectra indicate that SO2 promotes formation of oxygen vacancy on catalyst, leading to the reduction of Fe(III) into Fe(II). Compared with the ?OH generation via Haber-Weiss mechanism, the catalytic decomposition of H2O2 over "≡Fe" ("II" )"-OH" performs a higher ?OH generation rate and consumed less H2O2, indicating the promotion of SO2 on NO removal. With respect to the decreased NO removal efficiency in a 12 hours experiments, the results of SEM-EDX indicated that the agglomeration of Fe2(SO4)3 particle may be the main reason.
学术讨论
主办单位时间地点报告人报告主题
中国工程热物理学会 2014.11.01-03 中国西安陕西宾馆12号楼3楼会议室 吴波 变喷嘴间距撞击流吸收器湿法脱硫脱硝三维数值模拟
江苏省颗粒学会(江苏省颗粒学会青年科技(能源环境)论坛) 2015.11.08 南京市浦口高新开发区丽景路1号莱福城A区苏台合宴1楼百灵厅 吴波 基于氨基溶液吸收剂的烟气同时脱硫脱硝中试研究
东南大学 2016.03.05 东南大学礼西308 吴波 脱硫脱硝低碳化研究与思考
东南大学 2016.04.04 东南大学礼西308 吴波 脱硫脱硝一体化技术
东南大学 2014.11.08 东南大学动力楼429 John Edward Anthony Gasification Technology-Developments
东南大学 2015.06.25 东南大学动力楼429 Yong-Chil Se 燃煤烟气脱汞技术研究进展
东南大学 2015.06.28 东南大学吴健雄纪念馆报告厅 白俊文 第九届中国制冷竞赛技术交流
东南大学 2015.12.28 东南大学东南院102 宋启磊 Functional Nanomaterials for Energy and Sustainability
     
学术会议
会议名称时间地点本人报告本人报告题目
ICOPE 2015 - International Conference on Power Engineering 2015.11.29-12.4 Yokohama, Japan Simultaneous removal of SO2 and NOx using ammonia-based aqueous solution in a submerged circulative impinging stream reactor
14th International Conference on Environmental Science and Technology (CEST2015) 2015.09.03-05 Rhodes, Greece Simultaneous removal of SO2 and NOx using Amine-based aqueous solution in a pilot-scale liquid column tower
     
代表作
论文名称
Simultaneous removal of SO2 and NO from flue gas with ?OH from the catalytic decomposition of gas-ph
Removal of NO from flue gas using heat-activated ammonium persulfate aqueous solution in a bubbling
Enhancement of NO absorption in ammonium-based solution using heterogeneous Fenton reaction at low H
Simultaneous removal of SO2 and NOx using ammonia-based aqueous solution in a submerged circulative
 
答辩委员会组成信息
姓名职称导师类别工作单位是否主席备注
黄亚继 正高 教授 博导 东南大学
章名耀 正高 教授 博导 东南大学
袁竹林 正高 教授 博导 东南大学
卢平 正高 教授 博导 南京师范大学
朴桂林 正高 教授 博导 南京师范大学
      
答辩秘书信息
姓名职称工作单位备注
王沛 其他 讲师 东南大学